Known molding methods are not described in detail herein.
The invention relates more particularly to Liquid Composite Moulding (LCM) methods, which include various methods such as Vacuum Assisted Resin Transfer Moulding (VARTM), resin transfer moulding (RTM), liquid resin infusion (LRI), vacuum assisted process (VAP), or Seemann Composite Resin Infusion Moulding Process (SCRIMP) or any other method such as Combined Prepreg Infusion (CPI), Same Qualified Resin Transfer Moulding (SQRTM) or Controlled Atmospheric Pressure Resin Infusion (CAPRI). The invention is also suitable for Prepreg technology.
The most of these methods often share in common at least one step that consists in impregnating at least one layer of dry reinforcing fibers.
In the following the term “infusion” means that for instance a resin is sucked through a preform by applying vacuum and the term “injection” means that a resin is injected with additional pressure in a preform.
By way of example, the present invention relates to fabricating parts, e.g. parts of large dimensions or presenting complex structures, for which it can be difficult or even impossible to achieve a complete infiltration of resin or for which, in case of using different resins, the resin separation might be difficult. Another application of the invention is therefore the separation of different infusion and/or Prepreg resins.
Composite parts made using the above-mentioned methods, and in particular parts of large dimensions or of complex structure, may present mechanical properties that are locally inappropriate or insufficient. This gives rise for example to zones of weakness or to zones that present insufficient mechanical properties. A poor flow through the reinforcing fibers, e.g. as a result of unsuitable viscosity of the impregnation matrix, can give rise to such defects. When the flow of the impregnation matrix within the integral structure is not sufficiently under control, it can happen that e.g. the fibers are locally insufficiently impregnated.
In addition, the bonds between primary parts making up an integral structure often present shear strength and peel strength, that are insufficient. This applies for example when assembling panel elements and stiffening elements as happens in airplane fuselages.
In an attempt to solve this kind of problem, it is known to have recourse to various technical solutions. Thus, document U.S. Pat. No. 7,138,028 discloses depositing additional reinforcing layers in the bonding zones between the component parts of an integral structure. Because of the complexity of such structures, it becomes difficult to control the manufacturing so that one is faced with a major risk of not achieving the looked-for properties.
The integral structures obtained in that way are also not suitable for being easily repaired. As a general rule they need to be replaced in full even if only one of their component portions is damaged significantly. Smaller damages can be repaired, but do involve very complex repair methods due to bad accessibility for example.
Another technical solution, e.g. as disclosed in document EP 1 317 501, consists in using a thermoplastic sheet or a thermoplastic powder, for example, placed at the interface between primary parts making up an integral structure. The thermoplastic sheet has an influence on the properties of the impregnation matrix, encouraging it to diffuse within the fiber layer. Those integral structures are not suitable for being repaired. It is therefore necessary to replace them in full when severely damaged, even if only one of their component portions is damaged.
The composite parts obtained by known fabrication methods thus present the drawback that they can no longer be melted and reshaped for repair purposes.
The integration/assembly of different parts can also be achieved in a known way through riveting or bolting, causing holes in the structure and additional weight.